The present invention generally relates to vibration reduction systems in limited rotation motor systems, and relates in particular to mirrors for use with high speed limited rotation motor systems such as galvanometer scanning systems.
In typical galvanometer scanning systems a mirror is mounted to the output shaft of a limited rotation motor and the limited rotation motor is controlled by a control loop that seeks to cause the rotor of the motor, and therefore the mirror, to follow a position and velocity command waveform with arbitrarily high fidelity.
There are limits, however, on the fidelity with which the system may follow the command. For example, the acceleration of the mirror within the system is limited by the rate of rise of current in the motor windings. The positional precision is limited by the signal to noise ratio of the feedback method. The bandwidth of the system (which is its ability to move from position A to position B at a desired high velocity and to then settle at position B precisely in the shortest possible time), is limited primarily by vibrations in the moving parts. The bandwidth of the system will nominally be ½ the first torsional resonance in the moving structure.
It is customary, therefore, to make the moving parts as stiff as possible within the constraints of the allowable system inertia. Since the torque required of the motor to reach a specified acceleration is directly proportional to the inertia and is proportional to the current (whose rate of rise is limited as noted above), it is often the case that when the system parameters are optimized for a particular inertia, some component, typically the mirror, even when made of a very high stiffness-to-inertia material, is not as stiff as is required to reach system bandwidth goals. In this case, extra material is added to the mirror to increase its stiffness, but, at the cost of additional inertia, requiring a larger, more expensive motor as well as a control loop that is capable of driving the additional inertia.
There is a need therefore, for a limited rotation motor system that provides improved bandwidth without requiring a larger, more expensive motor and accompanying control system.